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From: dafa@ihwpt.UUCP (David Fay)
Newsgroups: net.micro.mac
Subject: Re: 1.5 Meg Upgrade from MacMemory
Message-ID: <509@ihwpt.UUCP>
Date: Thu, 10-Oct-85 14:40:48 EDT
Article-I.D.: ihwpt.509
Posted: Thu Oct 10 14:40:48 1985
Date-Received: Sat, 12-Oct-85 17:00:00 EDT
References: <501@ihwpt.UUCP> <2092@amdahl.UUCP>
Distribution: net
Organization: AT&T Bell Laboratories
Lines: 36

> I have had the Levco 2 Meg upgrade for over two months and I feel that
> memory > 512K makes a significant improvement to the Mac.  I am happy
> to see alternative sources of this type of upgrade.  However, there are
> a couple of items in the original article that puzzle me.
> 
> The more important item is the statement that the new Apple ROMs will
> relocate the screen buffer to the top of the 1.5 Meg address space.
> As address decode is a hardware, rather than software, function I would
> want a full and convincing explanation of this claim before I purchased
> the MacMemory upgrade.
> 
> The second item that did not seem quite right was the claim of a $200
> saving.  From the costs quoted this seemed to be true only if you bought
> more than 1 kit.  Unless you own more than one Mac this seems rather
> impractical.  If you have several Macs, you should also check Levco's
> quantity prices to determine what the real saving is.
> -- 
> Stephen J. Langdon                  ...!{ihnp4,cbosgd,hplabs,sun}!amdahl!sjl

	It is my understanding that the location of screen memory is
determined by a ScreenBase pointer that is placed in low memory.
I'm not sure how it gets there, but I would guess that there is a ROM
routine that figures out on boot up whether you have a 128K or 512K and
then puts the appropriate value in the pointer location. I don't see
why the Apple ROM couldn't figure out that you have 1 Meg, 2 Meg
or whatever and calculate where screen memory should be. Obviously Levco
does something like this with its ROM.
	The quantity prices apply to a single order. So if you want the lower
prices, find someone else that wants to place an order at the same
time.
-- 
--------------------
David Fay
AT&T Bell Laboratories
Naperville, IL 60566
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